Reaction milieu and afterburner incorporating same



G. R. SMITH May 7, 1963 REACTION MILIEU AND AFTERBURNER INCORPORATINGSAME Filed Feb. 6, 19 61 2 Sheets-Sheet l INVENTOR.

GORDON R. SMITH CM 4, gwr

' ATTORNEY May 7, 1963 G. R. SMITH 3,088,271

REACTION MILIEU AND AFTERBURNER INCORPORATING SAME Filed Feb. 6, 1961 2Sheets-Sheet 2 FIG.3

INVENTOR.

GORDON R. SMITH BY m/qsw ATIORNEY 3,088,271 REACTION MILIEU ANDAFTERBURNER INCORPORATING SAME Gordon R. Smith, St. Paul, Minn.,assignor to Minnesota Mining and Manufacturing Company, St. Paul,

Minn., a corporation of Delaware Filed Feb. 6, 1961, Ser. No. 87,380 6Claims. (Cl. 60-30) This invention relates to a new and novel structurefor defining a reaction milieu and to an article of manufacturecomprising the said structure in combination with a casing andassociated ducts to provide an afterburner for the exhaust of internalcombustion engines.

The incineration or burning of the residual combustibles present in theexhaust gases from internal combustion engines, particularly those fromautomobiles, is a desirable means of eliminating atmospheric pollution.It is rather surprising that ordinarily automobile exhaust gases stillcontain suflicient amounts of combustible substances so that, underconditions of elevated temperature (of the order of about 1200 to 1400F.) and with the addition of some additional air (typically of the orderof magnitude of about 10 to volume percent), the residual combustibleswill burn exothermically. This is analogous in some ways with theincineration of solid refuse and it is considered that that term is veryappropriate.

While the incineration of automobile exhaust gases is feasible from thethermodynamic consideration, the prior art apparently has not included acommercially practicuble device meeting the requirements of cost, spaceand efficiency. As a result of experiments in attempting to devise apracticable means for initiating and maintaining the incinerativecombustion of automobile exhaust gases, the conclusion has been reachedthat one of the major difliculties heretofore encountered lies inproviding a suitable container for the flame. For example, when thereaction is initiated in structures having a simple configurationconsisting of a multiplicity of small passageways in line with thedirection of flow, it appears that a large number of factors inherent inthe automobile exhaust gas system conspire to prevent maintenance of theflame in the structure. Such a structure is in fact rather like certaintypes of flame-arrestors, but slight fluctuations in pressure orlocalized conditions of pressure or temperature appear to result ineither enlargement of the flame front beyond the structure (withresulting collapse) or collapse before the structure. Whatever theactual reasons may be, such a structure does not continuously envelopand hold a stable flame, particularly in view of the pulsating nature ofautomobile exhaust gases and the variability of composition thereof.

It is an object of this invention to provide a structure having amultiplicity of extensively interconnected passageways, for continuouschemical reactions.

Another object of the invention is to provide a refractory structure forcontinuous gaseous chemical reactions involving high temperatures.

A further object is to provide a simple refractory structure capable ofmaintaining the sustained homogeneous incineration of automobileexhaust.

Another object of the invention is to provide an ef-. ficient refractoryflame-containing structure of relatively small dimensions.

A still further object of the invention is to provide an automobileexhaust afterburner.

Other objects of the invention will become evident from the disclosurehereinafter made.

It has been found that stabilization of a reaction zone in a reactor forgaseous reactants may be achieved by 3,fi88,27l Patented May 7, 1963extensive interconnection of passages of flow of the burning gas in astructure composed of corrugated sheets which contact each other only attheir ridges. By extensive interconnection is meant that theinterconnecting passageways are approximately equal in cross-sectionalarea to the passageways of flow themselves. The structure of theinvention thus is such that the passageways have continuous walls onlyalong one-half their diameter.

It has further been found that virtually ideal extensive interconnectionof passageways as the term is used herein is provided by stackingcorrugated sheets of material in superimposed array, with the axes ofthe corrugations of consecutive sheets in non-parallel arrangement. Asthe simplest such arrangement successive corrugated sheets are orientedwith the corrugations at right angles to those of the contiguouscorrugated sheets. However, from a practical standpoint this angle mayvary from about 20 to about 160, although angles of about 45 to aboutare preferred. Furthermore, a more or less random arrangement can bemade if desired, since the main consideration is the provision ofpassages by the contact of the ridges of adjacent sheets.

In order to provide the highly refractory structure which is required egfor combustion of exhaust gases,

the corrugated sheets must comprise either refractory materials such asceramics or be convertible thereto. The sheets can be adhered one toanother at the contact points, either by use of a binding cement or bysintering together at points of contact if desired. Alternatively theymay be stacked and held together by external means.

As will be described in greater detail below, the structures may beclassified generically as reaction milieus, since they can be used forchemical reactions involving gases, thus defining reaction zones forchemical reactions, e.g. exothermic or catalytic. The structures of theinvention have particular utility as flame holders, as in gas burnersand automobile exhaust-gas afterburners.

The heat resistance required of the ceramic or refractory material to beused in the structures is of course dependent upon temperatureconditions expected in a particular use. Thus, while for purposes of usein automobile exhaust gas afterburners, resistance to temperatures ofabout 1600 F. to perhaps 2000 F. is sought, the more readily availablematerials tend to limit the useful upper temperature limit of thestructure of about 1800 F. Materials which are unstable, or melt lowerthan the temperatures named are therefore unacceptable for constructionof an automobile exhaust gas afterburner, but may be useful in chemicalprocesses where maximum temperatures are lower. Also, for some purposesresistance to even higher temperatures may be imperative. Under suchcircumstances it is possible to employ refractory metals or moreheat-resistant ceramic ingredients. In general, in selecting additives,it is desirable to avoid the use of large amounts of ingredients whichmay flux the higher melting refractories with the formation of lowmelting phases. It will be apparent to one skilled in the ceramic artthat the numerous refractory ceramic materials available will enablechoice of desirable and useful materials. The known and availableceramic compositions are readily adaptable to use in the structures ofthe invention.

Representative sinterable ceramic materials useful for making corrugatedsheets for the purposes of this invention when relatively hightemperatures are encountered include such substances as alumina, siliconcarbide, beryllia, titania, zirconia, cordierite, mullite, petalite andthe like, as well as metal powders such as tungsten, molybdenum,tantalum and the like.

Formation of the structures of the invention as illustrated in thedrawings is readily accomplished according to the following procedure.

A raw material mix comprising the desired finely divided sinterableparticles and, if desired, plasticizing ingredients (such as, forexample, organic polymeric resins) and/or volatile viscosity adjustingmedia, is formed into a thin film or sheet material. Such film may beformed as thin as desired, e.-g. a mil or so, .as by knife coating on atemporarysupport, extrusion or the like as long as it possessessuflicient body when free of any viscosity adjusting fluids to retainits integrity during and after corrugation. Very thin, delicate filmsare hard to handle, whereas films thicker than about 0.125 inch tend tobe too bulky for convenient corrugation as described herebelow. Bestresults are obtained by avoiding extremes; and the advantages of thestructures of the invention with respect to strength and structureretention without fragility or fracture problems become particularlyapparent when using films about 2 to 50 mils thick. Advantageously, thinfilms contribute to the thermal shock resistance of the firedstructures, permitting them to withstand a multitude of rapid and severefluctuations in temperature without fracture.

In the step of corrugation itself, it may be desirable to support theplasticized green ceramic film on a thin sheet of metal foil, forexample, aluminum foil, preferably of a thickness on the same order ofmagnitude as the film to be corrugated (but usually not greater thanabout 0.01 inch), or to sandwich the green ceramic film between two suchmetal foil sheets as it is passed between the corrugating rolls,suitably at room or elevated temperatures. The [foil advantageouslyserves as a carrier to distribute corrugation stresses uniformly, aidingin obviating cracking or rupture of the films. Also, in the case ofthose films plasticized with ingredients which impart an elastic memoryproperty to the film, at least one sheet of metal foil corrugated withthe film is desirably left in position for a short time so as tomaintain the corrugation in the film and prevent reversion to a flatsheet.

Corrugation of the flexible films may be accomplished using standardcorrugating equipment, and without undue pressure at low temperatures.Usually corrugations of uniform periodicity are formed, for example,corrugations of repetitive and uniform wave shape, amplitude, andfrequency. The corrugations most frequently employed are those ofstandard curved ridges and grooves; however, other wave shapes orconfigurations may be useful. As a minimum requirement the amplitude ofcorrugations (that is, the elevation distance between the peak of aridge and the lowermost portion of an adjacent groove) is at least asgreat as the thickness of the film that is corrugated, which means thatthe elevation distance between the peak of a ridge on one side of -acorrugated film and the peak of a ridge on the opposite side of the filmis at least twice as great as the thickness of the film itself. However,the flame-containing structures of this invention, and particularly thepreferred structures in which the sheets are about 2 to 50 mils thick,generally have corrugations with amplitudes at least about five to tentimes greater than the thickness of the film and up to about twenty tothirty times this thickness. it is an important feature of thestructures of the invention that contact is provided at the points whereridges of adjacent sheets intersect. It will be understood that the termpoint is not employed in the mathematical sense, but in the practicalsense that contact is not continuous along the ridges but involves onlyvery small isolated areas. Adhesion at the points of contact where theridges of adjacent sheets intersect may be provided or contact may bemaintained by means urging the sheets together with sutficient force tomaintain structural relationship but not sufiicient to result inmechanic-a1 damage. Mechanical means for this purpose are readilyprovided, as by engagement with portions of a housing for thestructures, or bolts, encircling framework, clamps and the like. The

mechanical efiect of this pointwise adhesion is that the structures areless sensitive to thermal stress since expansion and contraction in anydirection does not result in abrasive action and can be absorbed by thecorrugated surfaces between points of adhesion.

.While the sinterable flexible plasticized corrugated films are in thegreen unfired state, they are cut and fabricated into assemblies andstructures such as illustrated in the drawings and described in thepresent specification or alternatively part of the final shapingoperations can be deferred until after assembly of the corrugatedmembers. At the points of contact between successive corrugated piecesadhesion may be provided by employing the basic raw material mix fromwhich the sinterable film or sheet material was formed, diluted withsuitable solvents or fluids to adjust viscosity, and then painted overthe ridges of the corrugations as a glue medium. The solvent of theapplied glue media may tend to solvate portions of the adjacentcorrugated members before volatilizing into the air. In any event, oncethe structure is dried, a temporary bond is formed at the points ofcontact which, after the structure is fired to sintering temperatures,turns into a strong and rigid weld. The extensively interconnectedpassageways are then bounded by successively adhered corrugated sheets.Alternatively, if desired, for some purposes, other temporary adhesivessuch as water glass may be employed which eifect slight fiuxing of theceramic material on firing. Of course where the sheets are not to becemented they can be stacked and held together mechanically.

In the green unfired state, the assemblies of corrugated sheets caneasily be cut or sawed to shape or trimmed as desired for thefabrication of the structures or they can be cemented together by themethods described above for the adhesion of successive sheets. By suchprocedures, orientation of the extensively interconnected passageways inany manner which may be desirable in the final structure is readilyachieved.

The completed green, unfired assembly is allowed to dry in air attemperatures up to about C. so as substantially to remove (volatilesolvents or organic fluids from its joints without affecting anythermoplastic binders or effecting any sintering of particles. Then thestructures are fired using temperatures suitable for a sintering of theparticular sinterable ingredients in the structure, as well understoodin the ceramic art.

Hereinabove has been generally described the manner of obtaining amultiplicity of extensively interconnected passageways in the reactionmilieu structures of the invention. The invention is further describedby reference to the accompanying drawings wherein:

FIGURE '1 is a side elevation of part of a structure possessingextensively interconnected passageways as hereinabove described.

FIGURE 2 shows an exploded View of a refractory annular flame-containingstructure of the invention consisting of only five sheets.

FIGURE 3 shows an exhaust-gas afterburner incorporating a refractoryannular flame-containing structure of the invention.

Referring to the drawings, in FIGURE 1 it will be seen that successivesheets 10, 12, 14 and 16 are arranged with the corrugations of eachsheet substantially at right angles to one another to producepassageways as at 11 interconnected as at 13. In this figure it will beseen that theconugations of sheets 10 and 14 are parallel and atapproximately right angles to the corrugations of sheets 12 and 16 whichare also parallel. The substantially point contactof the ridges of thecorrugations can also be noted as at 15.

FIGURE 2 shows an exploded view of an annular flame-containing structureconsisting of five sheets: 21, 23, 25, 27 and 2.9. 'In this figure itwill be apparent that none of the sheets are parallel with respect tothe corrugations. It would of course be within the scope of theinvention to have alternate sheets parallel in this respect. Theexternal and internal curved faces of the cylindrical structure formedby the stacked sheets will obviously be of different area and this is avaluable feature of the invention. The faces in which the passagesterminate in the structures of the invention consist generally of theopen portions of the interconnected passages and accordingly present apeculiar pattern produced by the thin edges of the component sheets.

FIGURE 3 shows a refractory annular flame-containing structure of theinvention positioned in a suitable container to provide an afterburnerfor automobile exhaust fumes. The mild steel casing 31 is divided into aplenum section 33 having inlet 35 and a burner section 37 separated byannular partition 39. Plenum section 33 is externally insulated by therefractory insulating covering 41 which is suitably made of fire clay.Burner section 37 is lined with a refractory in three pieces, viz.annular base plate lining 43 resting on and concentric with thepartition 39, cylindrical wall lining 44 concentric with the casing andinsulated from the vertical walls thereof by a packed fibrous insulationmaterial 45 and annular top plate lining 46 resting on the cylindricalwall lining 44. The refractory top plate is held in position by casingcover plate 47 having a centrally located outlet 51 and fastened to thesteel casing by bolts 48 through flange 49 of the casing. Concentricallylocated in the burner section and resting on base plate 39 is annularflame-container 53 which is held in position by superposed refractoryplate 55 and bolt 56 which extends downwardly to the exterior of thesteel casing. Other methods of positioning and retaining theflame-containing structure are equally suitable, as, for example byspring pressure from above. It is only necessary in this particularafterburner that the central hole in the flame holder be closed at theupper end so that gases entering at the lower end are forced to passradially outwardly through the flame container. The corrugations of thesheets of the flame-container 53 are drawn out of proportion. The sheetsare also shown in exaggerated thickness as the delineation of the scaleof edges and sections which are of the order of 2-50 mils in thicknessis not practicable. The central opening in the flame container is shownas the portion of the sheets not sectioned.

Not shown in this drawing are thermocouples used for test purposes toestablish the thermal gradients. The thermocouples are, of course, notnecessary for ordinary use. Supplementary air is conveniently introducedupstream in the exhaust line through port 34- so that adequate mixingoccurs in the plenum chamber. As ignition means a sparking plug 42 isused in chamber 37, preferably mounted in the annular space between theflame holder 53 and the lining 44. Alternatively preheating of theexhaust gases may be used as by direct flame from an auxiliary burner.

The annular overall cylindrical shape of the representativeflame-containing structure of the invention shown in exploded form inFIGURE 2 is to be considered as one embodiment of the invention. Thegeneral and overall configurations of these structures can be widelyvaried. Thus, the annular cylindrical form can be employed. For example,segments may be made on planes cutting parallel to the central axis ofthe cylinder radially at any angle or along chords of the circular areaor in planes not parallel to the axis and at right angles or otherwisethereto giving elliptical outlines or portions thereof. Such segmentsoffer the advantage that they provide a convenient means for providingflame-containing structures having predetermined dilferent areas of thefaces for inflow or combustible mixtures and outflow of exhaust gas.Such segments may further be cemented to one another, preferably in theunfired state, as hereinafter explained, to produce more complicatedshapes such as spherical, parabolic or hyperbolic. For cylindricalannuli of large radius, a number of smaller annuli can be cut intosegments with sides at angles representing radii of the larger structureand then assembled. The outer and inner surface will not be regularlycircular but this procedure may often prove more convenient thanconstruction of the larger structure. Sheets of square shape may also beemployed to build structures of box-like external configuration.

One characteristic feature of the flame-containing structures of theinvention which have central openings is that inlet and outlet facespossess different areas. It will be apparent that this feature isparticularly advantageous, when reaction such as combustion results inenlarged volumes of outgases.

An extremely useful feature of these structures is their radiativeability, which, coupled with their other features, presents greatadvantages. It will be seen that the outer surfaces of these structurespresent such an apparent enclosure of the inner structure owing to thenumerous curved surfaces that from a given point external and removedfrom the outer surface only relatively few of the passageways can beseen in cross-section as holes. It follows that heat is radiated to thatexternal point from all the other visible structure. The structureoperates to transmit the heat from the internal flame not only byconduction but very strongly by radiation.

The high radiative ability of structures of the invention can beemployed in reverberatory furnaces. Since the structures present verylittle resistance to flow of gases, they may be used to provideradiative surface where the use of flue openings has heretofore beennecessary. When composed of or coated with thermoluminescent materials,e.g. thoria, these structures provide an intense source of brilliantlight.

These structures further provide excellent supports for catalysts,particularly for gas phase reactions at elevated temperatures. Theextensive interconnection of the passageways assures turbulent flow andgood contact of gas with the catalyst-coated surfaces.

It is thus apparent that the cylindrical annular structures of theinvention possess a most useful and unprecedented combination ofproperties; namely, internal flame stabilization, low resistance to gasflow, high radiative ability and adaptibility in form.

The following specific examples are set forth to show the production ofuse of representative structure of the invention.

Example 1 Two refractory annular flame-containing structures designatedM-31 and M48 having respectively 7 and 4 /2 corrugations per inch arefabricated from flexible polymer-bonded sheets consisting essentially ofceramic particles which will combine during firing to approximately thecomposition of cordierite, and containing a few percent by weight ofcellulose fibers to enhance the green strength of the sheets.

The sheets are corrugated to the stated respective frequency by passagebetween mating corrugating rollers and are then cut into annular discshaving central holes 2 inches in diameter and 6 inches in outerdiameter. These discs are assembled in stacks, one stack being made ofthe sheets having 7 corrugations per inch and the other stack being madeof sheets having 4 /2 corrugations per inch. Successive discs aresuperimposed with corrugations at right angles. A slurry of the sameceramic particles with small additions of a phosphate flux and polyvinylalcohol as a binder is used as a temporary adhesive where corrugationstouch. The sheets are stacked to a total height of about 3.6 and 6inches respectively. The two green shapes thus produced are dried, andsubsequently fired at about 1350 C. for about 2 /2 hours. The ceramicparticles in the temporary binder become an integral part of thestructure on firing and hold it to- :gether.

The flame-containing structure designated M-ZS is mounted in anafterburner casing as shown in FIGURE 3 in which the plenum section isabout 11 inches in diameter and about 12 inches high and the burningsection (within the insulation and refractory) is 8 inches in diameterand inches high (exclusive of base and closing plates). Thermocouplesare positioned so there is one in the central hole, three locatedradially in the flamecontaining structure and one in the spaceperipheral to the structure to measure temperatures during operation.

Exhaust gases from a small test engine (output up to about 2.5 standardcubic feet per minute) are passed through the after'burner. Homogeneouscombustion is started by preheating the afterburner and shape with anauxiliary heater so that a temperature of 1400 F. is reached at thecentral part of the structure. At an input rate to the afterburner ofabout one standard cubic foot per minute and the addition of about 0.25s.c.f.m. of supplementary air plus a fraction (about one seventh) of theamount of raw gasoline entering the engine added to the exhaust gasesupstream from the plenum chamber, combustion continues within the flamecontainer as shown by the temperature readings.

Structure M-28 is removed and the structure designated M-31 is mountedin the casing and operated as above. The entrance ,gases contain about7% carbon monoxide and about 225 parts per million of hydrocarbons ashexane (determined by infra-red absorption spectrometry). The exit gasesafter burning containing substantially 0.0 percent carbon monoxide andno hydrocarbons as determined by this method. The flame is maintained inthe shape within limits of gas flow of about 0.5 to 1 s.c.-f.m. In viewof the elevated temperature necessary for perpetuation of combustionextremely low flow rates are not feasible in this instance.

Increased shielding of the flame-containing structure to lessen lossesdue to external radiation of heat is found to be desirable in someapplications. This is effected in one embodiment by mounting the annularflame-containing structure within a cylindrical insulated casing andproviding concentric inner passageways to efifect utilization of thesensible heat of the burned exhaust gases, and of the heat radiatedinwardly from the structure, to preheat the secondary air and theentering exhaust gases. A centrally located tube extends along the longaxis of the cylinder to form the exit passageway for the incineratedexhaust gases. Thus tube is surrounded by a passageway for secondary airwhich is added to the incoming exhaust gases, and is in turn surroundedby the ceramic structure. Exhaust gases to be burned enter an annularinlet plenum chamber at one end, from which they pass through a mixingthroat and mix with the preheated secondary air. The mixed gases enterthe flame-containing structure through the inlet annular passagewaysurrounding the passageway for secondary air, the exterior wall of thisinlet passageway being formed by the interior face of the ceramicstructure. This wall radiates heat to the other Wall thus furtherheating the secondary air. After burning in the flame-containingstructure, the burned gases pass outwardly to the space between theceramic shape and the cylindrical shell and enter the central exhaustpassageway by means of a plenum chamber and ports in the central exhaustpassageway at the end opposite the inlet end. A spark plug is fitted ata convenient point in the casing to provide for initial ignition.

An afterburner as above described is constructed having a cylindricalflame-containing structure consisting essentially of corrugated aluminumoxide sheets having 9 corrugations per inch with a central open-ing of 4inches internal diameter and 7.5 inches in external diameter, and 9inches long. This device is attached to the exhaust manifold of asix-cylinder automobile engine of 223 cu. in. displacement and 31.5 HP.(AMA rating). When the exhaust gases are first ignited by sparking inthe outermost annular space with the engine choked to give a richmixture, the temperature gradually rises and the flame moves back (upstream) into a flame-containing shape and is maintained there. Thecarbon monoxide content of the admitted gases is reduced from between3.5 and 6.5 percent by volume to values below 1.0 percent by volume.Under some conditions this value is even reduced below 0.25 percent. Thepressure drop across the afterburner is below 5 cm. of mercury.

Another embodiment of the invention is found to provide a useful burnerfor air and gas mixture and can be employed, for example, in a furnace.A refractory block, for example, of clay, about 3" x 4" x 8", isprovided which has a cavity about 1%" x 3" x 3" deep in one of the 3" x8 faces. A hole is bored to connect the cavity with an end of the block,and a suitable gas-air inlet connector is cemented into the bore. Aflame-containing structure of the invention having the form of a segmentof one of the above annular shapes is cemented into the cavity usingfire clay or furnace cement. The structure is out along radii 30 apartso that the cut faces are not parallel and consequently the innerconcave surface area is smaller than the outer convex surface area. 7 Agenerally wedge-shaped segment 3 inches long, about 1 inch thick(between the inner and outer curved surfaces) and about 2 inches wide atthe outer curved surface is thus prepared from an annular structure asdescribed above consisting substantially of cordierite after firing.

The cordierite segment is mounted so that it is embedded to aboutone-half its height in the cavity of the fire brick and the exposedsides are covered with sheets of cordierite, such as those employed inconstruction of the shape, or fire clay, etc., so that burned gasesemerge only from the convex face. A gas-air mixture is provided as aboveand the burner is ignited. The flame burns entirely Within thecordierite segment and radiates heat very effectively. Greater surfacefor radiation of heat can be provided by a shorter radius of curvatureof the convex surface or by otherwise altering the geometry of theshape.

In another embodiment of the invention, a chemical reaction is carriedout in the structure. This can be illustrated by a catalytic process,specifically the catalytic conversion of carbon monoxide to carbondioxide with platinum. This method is usefully employed to remove thecarbon monoxide from automobile exhaust gases. The conversion iseffected in the presence of platinum at temperatures above about 450 F.

A cylindrical stainless steel casing about 10 inches in diameter and 29inches long is constructed with an outlet connection at one end and acover plate having an inlet and catalyst mounting means at the other.The outer surface of the casing is provided with cooling fins. A structure according to the invention is made composed of stacked, corrugated,somewhat porous alumina disks, about 2.7 inches long and 5% inches indiameter, and with a central passageway 2 inches in diameter, the sheetsbeing adhered to each other at the point of contact. This structure istreated by soaking it in about 5% aluminum nitrate solution, followed byimmersing it in 20% aqueous ammonia and then heating to about 950 F.This sequence is repeated 12 times, to impregnate the ceramic with asuitable aluminum oxide base for the platinum catalyst. The structure isthen soaked in 0.03 M chloroplatinic acid solution and heated to formmetallic platinum. These steps can be carried out on the fired,corrugated ceramic disks before assembling them, if desired, but it ismore convenient to assemble the structure first. The catalytic structureis mounted on the cover plate of the casing with the central holepositioned in line with and connecting to the inlet opening. A plug isprovided in the central passageway at about 5 /2 inches from the inletend and the distal end of the passageway closed by a flat fire clay discof the same diameter as the catalytic structure. The unit is thenassembled in the casing with a circumferential annular partition whichalso serves as a support for the catalytic shape in the casing beinglocated about 12 inches from the inlet end. About two inches of headspace remains at the outlet end. The catalytic structure is mounted bymeans of suitable locating studs within the casing. The combination ofthe plug in the passageway and the annular support effectively makes theone catalytic structure into three sequential portions, so that the flowthrough the unit is first radially outward through the catalyticstructure, then radially inward and finally radially outward and then tothe outlet. The unit is employed as an afterburner on an internalcombustion engine. It is mounted in the exhaust gas stream about 8inches from the manifold; about 15% of secondary air is mixed with theexhaust gases before they enter the inlet of the afterburner. When thetemperature in the catalytic structure reaches about 475 F., catalyticand exothermic conversion of CO to CO starts. Since no preheater isprovided it is found that racing the engine substantially reduces thetime necessary to start reacting. The reaction becomes progressivelymore eflicient as the entire catalytic shape heats. The engine is runthrough cycles of idling, acceleration, cruising and deceleration for aprolonged period (equivalent to over 6,000 miles). The carbon monoxideis consistently reduced from the range of about 3 to 5 percent by volumeto no more than a few tenths of one percent and on parts of the cycle isusually less than 0.1 percent. The pressure drop through the catalyticstructure is very low. The catalytic oxidation of carbon monoxide to thedioxide is thus seen to be carried out very efliciently in the milieuprovided by the ceramic shape of the invention.

What is claimed is:

1. A milieu for gaseous reactions consisting of an assemblage of stackedsuperimposed refractory corrugated sheets, the axes of the corrugationsof adjacent consecutive sheets being non-parallel and the said sheetsbeing held in contact to each other only at the intersection of theridges of said adjacent sheets, the edges of said corrugated sheetsbeing aligned and collectively forming at least two faces, at least oneof the said faces being an inlet into said milieu for unreacted gasesand the remainder of said faces being an outlet for reacted gases; andmeans for introducing gases into said milieu via said inlet.

2. A flame container for gaseous combustion consisting of an assemblageof stacked superimposed refractory corrugated sheets, the axes of thecorrugations of adjacent consecutive sheets being non-parallel and thesaid sheets being in contact with and adhered to each other only at theintersection of the ridges of said adjacent sheets, the edges of saidcorrugated sheets being aligned and collectively forming at least twofaces, at least one of said faces being an inlet into said flamecontainer for unreacted gases and the remainder of said faces being anoutlet for reacted gases; and means for introducing gases into saidflame container via said inlet.

3. A flame container of generally cylindrical form con sisting of anassemblage of stacked superimposed refractory corrugated discs providedwith a central aperture, the axes of the corrugations of consecutivediscs being non-parallel and the said discs being urged together andcontacting each other only at the intersections of the ridges ofadjacent sheets, the edges of said discs and of said central aperturesbeing aligned and collectively forming an exterior face and an interiorface, respectively, of said assemblage; the interior face being an inletinto said flame container for unreacted gases and the exterior face ofsaid assemblage being an outlet for reacted gases and a means comprisingthe passageway defined by the said interior face for introducing gasesinto said flame container.

4. A flame container of generally cylindrical form consisting of anassemblage of stacked superimposed refractory corrugated discs providedwith a central aperture, the axes of the corrugations of consecutivediscs being non-parallel and the said discs being adhered together andcontacting each other only at the intersections of the ridges ofadjacent sheets, the edges of said discs and of said central aperturesbeing aligned and collectively forming an exterior face and an interiorface, respectively, of said assemblage; the interior face being an inletinto said flame container for unreacted gases and the exterior face ofsaid assemblage being an outlet for reacted gases and a means includingthe passageway defined by the said interior face for introducing gasesinto said flame container.

5. An afterburner for automobile exhaust gases having acombustion-supporting content of oxygen comprising, in combination,

A. a casing provided with an inlet for said exhaust gases and an outletfor said gases after combustion thereof,

B. means for initiating combustion of the said exhaust gases and,

C. a flame-container, positioned within said casing so as to betraversed by said gases after initiation of combustion, consisting of anassemblage of stacked superimposed refractory corrugated sheets, theaxes of the corrugations of adjacent consecutive sheets beingnon-parallel and the said sheets being in contact with each other onlyat the intersections of the ridges of adjacent sheets.

6. An afterburner for automobile exhaust gases having acombustiomsupporting content of oxygen comprising, in combination,

A. -a casing provided with inlet and outlet means for said exhaustgases,

B. means for initiating combustion of the said exhaust gases and,

C. a flame-container, positioned within said casing so as to betraversed by said gases after initiation of combustion, consisting of anassemblage of stacked superimposed refractory corrugated sheets, theaxes of the corrugations of adjacent consecutive sheets beingnon-parallel and the said sheets being adhered in contact with eachother only at the intersections of the ridges of adjacent sheets.

References Cited in the file of this patent UNITED STATES PATENTS1,771,439 Hyatt July 29, 1930 1,789,226- Ensign et al Jan. 13, 19311,789,812 Frazer Jan. 20, 1931 1,839,880 Hyatt Jan. 5, 1932 2,682,304Kennedy June 29, 1954

1. A MILIEU FOR GASEOUS REACTIONS CONSISTING OF AN ASSEMBLAGE OF STACKED SUPERIMPOSED REFRACTORY CORRUGATED SHEET, THHE AXES OF THE CORRUGATIONS OF ADJACENT CONSECUTIVE SHEETS BEING NON-PARALLEL AND THE SAID SHEETS BEING HELD IN CONTACT TO EACH OTHER ONLY AT THE INTERSECTION OF THE RIDGES OF SAID ADJACENT SHEETS, THE EDGES OF SAID COR- 